1. Field of the Invention
The present invention relates generally to rotation sensor devices for sensing the rotation of an electric motor, and more specifically to an improved magnetic rotation sensor device responsive to changes in magnetic field intensity.
2. Discussion of the Prior Art
Self-controlled synchronous motors is the name generally applied to thyristor motors and transistor motors well-known in the art. These brushless DC motors require a rotation sensor device in order to sense the angular position of the motor shaft and subsequently control the conduction of thyristors and transistors involved to ensure the proper sequential energization and de-energization of the armature windings in the motor.
In conventional self-controlled synchronous motors a position sensor senses the actual position of the rotor of the motor and provides a position signal to a phase control circuit. The phase control circuit responds to the actual position signal and controls the conduction of transistors or thyristors which permit the energization and de-energization of the armature windings in the motor. Conventional rotation sensor devices, as discussed above, have included photo-optic arrangements in which a light beam is interrupted by movement of the rotor so as to provide a position signal. Other rotation sensor devices include a magnetic field movable wlth the rotor in combination with a Hall effect device for sensing the movement. Also resolvers, synchros and potentiometers ncan be used to provide a rotor position signal. PG,3
U.S. Pat. No. 4,329,636 to Uchida et al issued May 11, 1982 teaches one such rotation sensor device with a rotor having a magnetic pole disposed thereon and a magnetic sensor element for sensing increases and decreases of magnetic flux density due to rotation of the rotor. A control circuit separates position signal information from speed signal information and controls the conduction of associated thyristors which in turn control the sequencing of current pulses applied to the armature windings of the motor.
The prior art rotor position sensing devices have inherent problems which the present invention addresses. The Hall effect devices tend to over-heat and require a substantial volume, rendering motors equipped with such sensors larger, bulkier, and more expensive, than is desirable. Optical encoders are subject to diode failure and photo-sensitive transistor failure. In addition, a coating or film of dust or debris can interfere with the light transmission properties. Resolvers, synchros and potentiometers all require significant added volumes with substantail additional complexity, the most important of which is the requirement for separate electrical excitation.